Cirrus Logic Bundle Assignments in CobraNet Systems User Manual

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Bundle Assignments in CobraNet

TM

Systems

Ray Rayburn, Cirrus Logic, Inc.

Within a CobraNetTM network, all audio channels are packaged into groups called Bundles (formerly called
Network Channels) for transmission. The default bundle configuration uses 8 audio channels of 20 bit
sample size. 8 audio channels per bundle is the maximum size possible, although using fewer audio
channels is permitted. For most efficient utilization of network bandwidth, use of maximum size Bundles is
suggested when possible. In the rest of this document we will be talking about maximum size Bundles.
Other bundle configurations are also possible which use 16 or 24 bit samples. When 24 bit audio channels
are used with a sample rate of 48-kHz, only 7 audio channels can be packaged into a single bundle due to
packet size limitations imposed by the Ethernet standard.

A CobraNet
or more CobraNet
the network conductor based on a priority scheme. The Conductor indicator will light on the CobraNet

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network is coordinated by one of the devices operating in the role of conductor. When two

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devices are interconnected properly, one of the devices will be automatically elected

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device that is serving as the conductor.

Each CobraNetTM device has the ability to send and receive a fixed number of Bundles. The Bundle number
tells the CobraNetTM conductor which specific CobraNetTM device is trying to communicate with which
other CobraNetTM device(s) over the network. Use of Bundle numbers removes the necessity of the user
having to tell the devices the Ethernet hardware addresses of the other devices with which it is trying to
communicate. As long as the CobraNetTM devices are all set to the same Bundle number, the CobraNetTM
system takes care of all the rest of the technical details of setting up an audio path over Ethernet between
the devices.

A given Bundle may have only one transmitter that places it onto the network. Unicast Bundles may have
only a single receiver. Multicast Bundles may have multiple receivers.

Ethernet networks can be built using either repeater hubs or switching hubs. A repeater is a half duplex
device which takes the data that comes into each port, and sends it back out all ports except the port in
came in on. A switch is a full duplex device which accepts data coming in each port and stores it until it can
examine the addressing of each packet of data. If the incoming data has a multicast destination address, it
then sends the data out all ports except the one it came in on. If, however, the data has a specific destination
address the switch only sends it out the port which is connected to the matching address. In an ordinary
Ethernet data network it is possible to mix both types of devices and have the network continue to work.
This is not the case with CobraNet
switches. However, non-CobraNet

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A CobraNetTM network requires use of either all repeaters or all

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devices may be attached to a switched CobraNetTM network via a

repeater.

On a repeater (hub based) network, there is a fixed maximum of 8 Bundles per network. Any Bundle may
be placed onto the network from any port, and will appear at every other port on the network. The Bundles
usually used in a repeater network are numbered in the range from 1 to 255, and are called Multicast
Bundles. Such channels are always transmitted in a multicast mode, and may be received by any of the
CobraNetTM devices on the network.

As long as the limit of 8 total Bundles is not exceeded, it does not matter which channel numbers in the
range of 1 to 65,279 are used.

Use of switched hubs (or switches) is recommended when mixing computer data and CobraNet

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on the

same network. Use of repeater hubs is strongly discouraged as audio dropouts may occur.

Bundle Assignments Ap Note Rev. 1.0 ©Copyright 2004 Cirrus Logic, Inc

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On a switched network, there is no fixed maximum number of Bundles possible. The number will be
determined by the network design. Again, Bundles from 1 to 255 are Multicast Bundles and, since they are
multicast, will usually be sent to every port in the network. It is not suggested to use more than 4 multicast
Bundles in a switched CobraNetTM network. There are special cases where more could be used, which we
will go into later.

Bundles from 256 to 65,279 are called Unicast Bundles. These are addressed to a single destination unit
and are sent Unicast. A switch will send these channels only out the ports leading to the CobraNet

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device
they are addressed to. Unlike Multicast Bundles, Unicast Bundles will not be transmitted unless a receiver
is requesting that channel. This allows destination controlled routing, where the receiver selects one of
several possible transmitters to receive, and only the selected transmitter is activated.

It is possible to have far more than 8 total Bundles active on a switched network if most of those channels
are sent unicast using Unicast Bundles. A given port on a Fast Ethernet switch can only send 8 Bundles out
without running out of bandwidth. Those Bundles will consist of every Multicast Bundle on the network,
plus any Unicast Bundle addressed to a CobraNet

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device connected either directly or through other

switch(s) to this port on the switch.

Some switches have Gigabit Ethernet ports in addition to the Fast Ethernet ports. The Gigabit ports can be
used to transfer data between switches with 10 times the bandwidth of a Fast Ethernet port and can carry
ten times as many Bundles as Fast Ethernet can.

CobraNet

TM

over a switched network allows coexistence with ordinary computer data on the same network,
as there are few or no collisions possible. There is the possibility that CobraNetTM traffic on the network
will cause problems for 10 Mbit Network Interface Cards (NICs) used for computer data traffic. Recall that
Multicast Bundles are sent to all nodes in the same network. Since 8 Bundles will fill a Fast Ethernet (100
Mbits) switch port, if that port is connected to a 10 Mbit NIC (most Fast Ethernet switch ports are dual
speed 10/100 ports) then it is easy to see that multicast data from CobraNet

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can saturate the 10 Mbit NIC

and cause it to drop packets.

There are several possible solutions:

• Use a 100 Mbit NIC. The 100 MBit interface standard is both faster and operates in full duplex
mode.

• Use few, if any, Multicast Bundles.

• Use a Managed Switch. Most managed switches have multicast filtering features. These allow you

to exclude multicast traffic from a specified port. If your data is carried by the Internet protocol
(IP), it is usually safe to filter all multicast traffic except the FF:FF:FF:FF:FF:FF destination
address used by the address resolution protocol (ARP) associated with IP.

• Use separate physical networks for audio and data.

• Uses VLANs. VLANs are supported by most managed switches and allow the creation of

logically separated networks. This provides the benefit of separate networks while using the same
network infrastructure. All traffic in a given VLAN, even multicast traffic, is isolated to only those
ports which are part of the VLAN. You can typically partition multiple VLANs and assign ports to
them as needed. In addition, uplink ports used to connect multiple switches can typically be
configured to route VLAN traffic between switches allowing creation of a VLAN that can span
multiple switches.

• VLANs can also be used in some cases when you need to use more Multicast Bundles than is
allowable on a given CobraNet
have the ability to run twice as many Multicast Bundles.

• Use multi-unicast bundles. Another solution that can be used with some CobraNet
transmitting the same audio information on two, three, or four Unicast Bundles to specific
destinations instead of a single Multicast Bundle. Please note that legacy CobraNet

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network. By splitting the network into two virtual networks you

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devices, is

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devices may

not have this capability. Some devices can only transmit 2 Bundles, while others can transmit 4.

Bundle Assignments Ap Note Rev. 1.0 ©Copyright 2004 Cirrus Logic, Inc

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